Tone device having positive feedback common emitter amplifier

ABSTRACT

The tone of a call tone device is produced by a positive feedback common emitter amplifier and transducer arrangement. Voltage supply to the tone generator is interrupted cyclically by an astable multivibrator with timer circuit to provide an intermittent call tone.

United States Patent 1 Lawson et al.

11 3,742,491 [4. June 26,1973

TONE DEVICE HAVING POSITIVE FEEDBACK COMMON EMITTER AIVIPLIFIER Inventors: Peter James Lawson,

Shoreham-by-Sea; Ferenc Kocsis, Hove, both of England A. P, Besson,& Partner Limited, Hove, England Filed: Dec. 14, 1970 Appl. No.: 97,486

Assignee:

Foreign Application Priority Data Nov. 13, 1970 Great Britain 54,173/70 US. Cl .1 340/384 E, 340/384 R Int. CL, G08b 3/10 Field of Search 340/384 E [56] References Cited UNlTED STATES PATENTS 3,341,841 9/1967 Stampfli 340/384 E 3,341,842 9/1967 Breguet 340/384 E 3,346,857 10/1967 Cromer 1. 340/384 E 3,009,099 11/1961 Muller 1 340/384 E 3,108,597 10/1963 Moss 340/384 E Primary ExaminerHarold l. Pitts Attorney-Webster B. Harpman [57] ABSTRACT The'tone ofa call tone device is produced by a positive feedback common emitter amplifier and transducer arrangement. Voltage supply to the tone generator is. interrupted cyclically by an astable multivibrator with timer circuit to provide an intermittent call tone.

6 Claims, 3 Drawing Figures are 9 Patented June 26, 1973 2 Sheets-Shoat 1 FIG] FIG. 2

Patented June 26, 1973 3,742,491

2 Sheets-Sheet 2 TONE DEVICE HAVING POSITIVE FEEDBACK COMMON EMITTER AMPLIFIER BRIEF SUMMARY OF THE INVENTION This invention relates to call tone devices, by which term it is intended to mean a device which functions to produce a tone output which may be used under the following circumstances, given by way of non-limiting example:

Industrial enunciators, alarm and warning systems,

e.g. level indication;

Medical patient monitoring systems, e.g. pulse rate monitoring:

Military the production of call tones for radio or telephone equipment or monitoring of special security systems;

Domestic as a room or door bell or in burglar alarm systems.

This invention seeks to provide a compact call tone device, for use in the radiation of tones within a wide frequency band, and to provide such device which may produce an intermittent tone.

In accordance with the present invention there is provided a call tone device with provision for intermittent tone output, the device comprising a call tone generator and an interrupter; the said generator comprising acommon emitter transistor amplifier and a transducer having a main winding connected between the transistor collector and a voltage supply and a secondary winding connected into the base circuit of the transistor in opposite phase to the said main winding; and the said interrupter comprising an astable multi-vibrator operative to control energisation of the said tone generator.

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 illustrates a circuit of a call tone generator;

FIG. 2 illustrates a circuit of an interrupter; and

FIG. 3 illustrates in exploded view the construction of a device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 there is shown a common emitter amplifier circuit with the main winding 100 of a transducer TDl connected between the collector of a transistor T1 and a supply voltage of any convenient value, e.g. 12 volts DC or 9 volts DC. Conveniently the transducer TDl functions in accordance with the known rocking armature principle and therefore no descriptive reference will be made hereinafter to the function of this transducer.

A feedback or secondary winding 101 of the transducer TDI is connected into the base circuit of the transistor T1 in opposite phase to the main winding 100 thereby to create positive feedback. Oscillation will therefore occur when there is energisation by the aforementioned supply.

Resistors Rl, R2 and R3 are provided and function as bias resistors, R3 functioning also as a voltage feedback resistor to minimise distortion.

If desired a supplementary capacitor may be provided as indicated in broken lines at C1. This capacitor C1 serves to filter out unwanted frequencies.

The circuit of FIG. 1 thus generates a call tone. This call tone is interrupted by means of the interrupter circuit of FIG. 2, such interruption being by electronic means, i.e. without the need to rely on mechanical contacts. The interruptions produced by the circuit of FIG. 2 are at fixed intervals and the interruption intervals may be varied over a wide range.

As shown in FIG. 2, the interrupter circuit comprises an astable multivibrator with a timer circuit incorporating complementary transistors T20 and T30. The call tone generator is located in the collector circuit of T30 as indicated at CTG. An additional transistor T10 is provided in conjunction with a resistor R20 to control the mark-space ratio.

When a suitable supply voltage is connected, e.g. 9 or 12 volts DC, the capacitor C10 charges in series with T20 which switches on, due to the charging current. T30 then becomes conductive due to the action of T20 and with T30 conductive, the call tone generator located in the collector circuit of T30 is energised.

It is also the case that with T30 conductive, T10 is switched off owing to the low collector voltage or saturation voltage at T30.

The charging current of C10 then drops and as this happens T20 becomes non-conductive. The multivibrator will then transfer to its alternative state with the result that T30 is switched off. Thus the call tone generator at CTG is de-energised and the tone output of the device will disappear.

The voltage at the collector of T30 then increases and T10 becomes conductive. Capacitor C10 is discharged through resistors R20, R30 and the collector/emitter path of T10. When the discharge of C10 is complete, T20 again becomes conductive.

This cycle then repeats until such time as the supply is completely removed, i.e. when the device is switched off.

It should be noted that the resistor R30 controls the time period during which the generator is switched on and the off period is govened by the resistor R20. If desired these and other components may be rendered variable to facilitate control of the periods that depend thereupon.

It should be noted that the diode D10 shown in the circuit of T20 is for reverse voltage protection and it should be further noted that supplementary resistor R10 may be introduced as illustrated in FIG. 2 to ensure constantcurrent consumption during the off period of the operating cycle.

Conveniently, as illustrated in FIG. 3, the call tone device of the invention is formed as a compact three terminal integrated unit. Such a unit comprises a case (1) with terminal tags (2), (3) and (4). The case (1) embraces a printed circuit board (5) on which are mounted the components of the interrupter; an insulator (6) and suitable securing nuts and screws (7) are also provided.

At (8) there is provided a cover which embraces a further printed circuit board (9) on which are mounted the tone generator components; also provided are a yoke and magnet (10), a coil (11), an armature (12), a diaphragm (13) and frame (13a), a front plate (14) and plate cover (15). Also provided, as shown in the exploded view of FIG. 3, are suitable screws, nuts and terminal mouldings (16) for securing the arrangement together. Also used to secure a connecting rod (17) for the diaphragm is a suitable bonding agent such as Araldite (Trade Mark).

It will thus be evident that in the exploded illustration of FIG. 3 the call tone generator including the sound producing diaphragm may be regarded as lying to the left of the notional dividing line AA and the interrupter circuit may be regarded as lying to the right of the said line.

When assembled, the interrupter circuit and soundproducing diaphragm part is mounted on top of the call tone generator part so as to be co-extensive thereof.

Various modifications of the invention may be made within the scope of the appended claims.

What we claim is:

l. A call tone device with provision for intermittent tone output, the device comprising a call tone generator and an interrupter; the said generator comprising a common emitter transistor amplifier and a transducer having a main winding connected between the transistor collector and one terminal of a voltage supply and a secondary winding connected into the base circuit of the transistor in opposite phase to the said main winding; and the said interrupter comprising an astable multivibrator operative cyclically to interrupt the voltage supply to said tone generator.

2. A call tone device according to claim 1 wherein the electrical circuit components are associated on printed circuit boards housed with a tone producing diaphragm in a common case.

3. A call tone device as defined in claim 1 wherein said call tone generator includes a pair of biasing resistors connected as a voltage divider between said one terminal of said voltage supply, a capacitor and a charging resistor connected in series between the base of said one complementary transistor and said supply terminal of the interrupter, a further transistor and a discharging resistor connected to the base of said one complementary transistor and through the emittercollector path of said further transistor to said other terminal of the voltage supply, and a further biasing resistor connected to the base of said further transistor and said supply terminal of the interrupter.

4. A call tone device according to claim 3 wherein a supplementary capacitor is connected across the transistor emitter and collector in series with a said voltage feedback resistor, thereby to filter out unwanted frequencies.

5. A call tone device according to claim 3 wherein said resistors are variable.

6. A call tone device device according to claim 3 wherein a supplementary resistor is connected between terminal of said voltage supply and a supply terminal of said interrupter, said secondary winding being connected to the juncture of said resistors, a voltage feedback resistor connected between the emitter of said transistor amplifier and said interrupter; and wherein said one terminal of the voltage supply and the emittercollector-path of said further transistor to ensure constant current consumption during the off period of the multivibrator operating cycle. 

1. A call tone device with provision for intermittent tone output, the device comprising a call tone generator and an interrupter; the said generator comprising a common emitter transistor amplifier and a transducer having a main winding connected between the transistor collector and one terminal of a volTage supply and a secondary winding connected into the base circuit of the transistor in opposite phase to the said main winding; and the said interrupter comprising an astable multivibrator operative cyclically to interrupt the voltage supply to said tone generator.
 2. A call tone device according to claim 1 wherein the electrical circuit components are associated on printed circuit boards housed with a tone producing diaphragm in a common case.
 3. A call tone device as defined in claim 1 wherein said call tone generator includes a pair of biasing resistors connected as a voltage divider between said one terminal of said voltage supply and a supply terminal of said interrupter, said secondary winding being connected to the juncture of said resistors, a voltage feedback resistor connected between the emitter of said transistor amplifier and said interrupter; and wherein said interrupter comprises a pair of complementary transistors constituting said astable multivibrator, one of said complementary transistors having its emitter-collector path connected between said one terminal of the voltage supply and the base of the other complementary transistor, the other complementary transistor having its emitter-collector path connected between said supply terminal of said interrupter and the other terminal of said voltage supply, a capacitor and a charging resistor connected in series between the base of said one complementary transistor and said supply terminal of the interrupter, a further transistor and a discharging resistor connected to the base of said one complementary transistor and through the emitter-collector path of said further transistor to said other terminal of the voltage supply, and a further biasing resistor connected to the base of said further transistor and said supply terminal of the interrupter.
 4. A call tone device according to claim 3 wherein a supplementary capacitor is connected across the transistor emitter and collector in series with a said voltage feedback resistor, thereby to filter out unwanted frequencies.
 5. A call tone device according to claim 3 wherein said resistors are variable.
 6. A call tone device device according to claim 3 wherein a supplementary resistor is connected between said one terminal of the voltage supply and the emitter-collector path of said further transistor to ensure constant current consumption during the off period of the multivibrator operating cycle. 